Droplet ejection devices are used for a variety of purposes, most commonly for printing images on various media. They are often referred to as ink jets or ink jet printers. Drop-on-demand droplet ejection devices are used in many applications because of their flexibility and economy. Drop-on-demand devices eject one or more droplets in response to a specific signal, usually an electrical waveform, or waveform, that may include a single pulse or multiple pulses. Different portions of a multi-pulse waveform can be selectively activated to produce the droplets.
Droplet ejection devices typically include a fluid path from a fluid supply to a nozzle path. The nozzle path terminates in a nozzle opening from which drops are ejected. Droplet ejection is controlled by pressurizing fluid in the fluid path with an actuator, which may be, for example, a piezoelectric deflector, a thermal bubble jet generator, or an electrostatically deflected element. A typical printhead has an array of fluid paths with corresponding nozzle openings and associated actuators, and droplet ejection from each nozzle opening can be independently controlled. In a drop-on-demand printhead, each actuator is fired to selectively eject a droplet at a specific target pixel location as the printhead and a substrate are moved relative to one another. A droplet's mass is distributed in the head and tail of the droplet. The head of the droplet lands on the target initially with the tail of the droplet subsequently landing on the target. Because drop-on-demand ejectors are often operated with either a moving target or a moving ejector, variations in droplet velocity lead to variations in position of drops on the media. These variations can degrade image quality in imaging applications and can degrade system performance in other applications. Variations in droplet volume and mass lead to variations in spot size in images, or degradation in performance in other applications.